Field of the Disclosure
Embodiments of the present application relates to the art of a drive unit of a hybrid vehicle having an engine, two motors and a power distribution device, in which an operating mode is switched by manipulating clutches to change a power transmission route.
Discussion of the Related Art
PCT international publication WO 2013/114595 describes a hybrid vehicle driving apparatus. In the driving apparatus taught by WO 2013/114595, a power distribution device and a first motor are arranged coaxially with an engine. A countershaft extends parallel to a common rotational axis of the power distribution device and the first motor to deliver drive force from the power distribution device to a differential mechanism through the countershaft. A second motor is disposed parallel to the countershaft so that an output torque of the second motor is also delivered to the differential mechanism through the countershaft. According to the teachings of WO 2013/114595, the power distribution device is comprised of two sets of planetary gear mechanisms, and a travel mode of the driving apparatus is shifted by altering a connection between rotary elements of the planetary gear mechanisms
PCT international publication WO 2011/138892 also describes a driving apparatus for a hybrid vehicle. In the driving apparatus taught by WO 2011/138892, an engine is connected to a first motor through a speed increasing mechanism, and to a second motor through a speed reducing mechanism. A first clutch is disposed between a ring gear of the speed increasing mechanism and an output gear, and a second clutch is disposed between the engine and the output gear. According to the teachings of WO 2011/138892, an operating mode of the driving apparatus may be shifted by manipulating the clutches among a series hybrid mode in which the second motor is driven by a power generated by the first motor, an engine directly-connected High mode, and engine directly-connected Low mode.
According to the teachings of WO 2013/114595, not only a hybrid mode (or a series parallel mode) in which an engine power is partially converted into an electric power to be supplied to the second motor to propel the vehicle, but also an electric vehicle mode in which the second motor or both of the first and the second motors are driven by an electric power supplied from a battery to propel the vehicle may be selected in the driving apparatus. However, a series mode in which the first motor is rotated by the engine and the second motor is driven by an electric power generate by the first motor to propel the vehicle is not available in the driving apparatus taught by WO 2013/114595. In the driving apparatus taught by WO 2011/138892, on the other hand, the speed increasing mechanism can be disconnected from the output gear that is connected to the second motor through the speed reducing mechanism, and hence the series mode is available. However, in the driving apparatus taught by WO 2011/138892, both of the speed increasing mechanism and the speed reducing mechanism are planetary gear units, and one of rotary elements of each of the planetary gear unit is fixed. That is, those planetary gear units are not allowed to distribute the engine power to the output gear and to any of the motors, and hence the series parallel mode is not available in the driving apparatus taught by WO 2011/138892.
In the hybrid vehicle, an operating mode is shifted by manipulating clutches to change a power transmission route. That is, the driving apparatus taught by WO 2013/114595 is allowed to establish the series mode and the driving apparatus taught by WO 2011/138892 is allowed to establish the series parallel mode by arranging an additional clutch in those driving apparatus. However, the driving apparatus enlarged by the additional clutch may not be fitted easily into the hybrid vehicle. Thus, it is difficult to increase available operating modes of the driving apparatus without enlarging the structure of the driving apparatus.